1. Photosynthesis!

2. Obtaining NRG Autotrophs Heterotrophs
Use NRG from the sun to make organic compounds
Heterotrophs
Must get NRG from food instead of directly from sunlight

3. ATP=NRG! ATP= adenosine triphosphate
ATP is the molecule that DIRECTLY provides NRG to do cellular work
Chemical NRG from organic molecules is transferred to ATP

4. ATP ATP is made up of five parts: The sugar= ribose The base= adenine
3 phosphate groups

5. ATP cont. When ATP loses the 3rd phosphate: NRG is released
This NRG is used by the cell
ADP is left

6. NRG Conversion

7. Obtaining NRG PHOTOSYNTHESIS
Converts light NRG from sun into chemical NRG
Series of reactions known as biochemical pathways

8. Photosyn. Overview
The oxygen (O2) and some organic compounds produced by photosynthesis are used by cells in process called cellular respiration.

9. Chloroplasts Chloroplasts have double membranes Outer Membrane
Separates chloroplast from
cytoplasm
Thylakoids
Inner membranes
Numerous
Grana
Stacks of thylakoids
Stroma
Fluid-like space

10. Overview cont. Photosynthesis can be divided into two stages:
LIGHT REACTIONS
Light NRG is converted to chemical NRG
Temporarily stored in ATP and the NRG carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate- oxidase)
CALVIN CYCLE
Organic compounds are formed using CO2 and the chemical NRG stored in ATP and NADPH

11. Photosynthesis Equation

12. Capturing Light NRG
The light reactions begin with the absorption of light in chloroplasts
Found in cells of plants, some bacteria, and algae

13. Capturing Light NRG Light and Pigments
White light from the sun is composed of an array of colors called the visible spectrum
Pigments:
Absorb certain colors of light and reflect or transmit the other colors

14. Capturing Light NRG Chloroplast Pigments:
Located in the membrane of the thylakoids are several pigments:
1. Chlorophylls: chlorophyll a and chlorophyll b
2. Carotenoids: yellow, orange, and brownish

15. Light NRG to Chemical NRG
PHOTOSYSTEM:
Grouped clusters of a few hundred pigment molecules in the thylakoid membrane
By absorbing light, pigment molecules in the photosystems (I and II) acquire some of the NRG carried by the light

16. Steps 1 and 2
In each photosystem, the acquired NRG is passed quickly to other pigment molecules until it reaches a specific pair of chlorophyll a molecules.
The acquired NRG forces electrons to enter a higher NRG level in the two chlorophyll a molecules of photosystem II
These excited electrons now have NRG to leave the chlorophyll a.

17. Step 3
The acceptor of these electrons from photosystem II is called the primary electron receptor, which donates the electrons to the electron transport chain.
Electrons move from molecule to molecule, losing most of the acquired NRG!
The NRG they lose is used to move H+ into the thylakoid

18. Light Rxn

19. Step 4
Light is absorbed by photosystem II at the same time it is absorbed by photosystem I.
Electrons move from chlorophyll a to another primary electron receptor.
Electrons lost from chlorophyll a are replaced by electrons that have passed through the electron transport chain from photosystem II.

20. Step 5
Electrons are then donated to another chain, which brings the electrons to the side of the thylakoid membrane that faces the stroma.
In the stroma, the electrons combine with a proton and NADP+. This causes the NADP+ to be reduced to NADPH.

21. Electron Replacement
Electrons from photosystem II replace electrons that leave photosystem I.
Replacement electrons are provided by the splitting of water molecules
For every two water molecules that are split, four electrons become available

22. Products?
Oxygen produced when water molecules are split diffuses out of the chloroplast and leaves the plant!

23. Light to Chemical NRG Making ATP in Light Reactions:
Light reactions produce ATP through chemiosmosis!
During chemiosmosis, the movement of protons through ATP synthase into the stroma releases NRG, then used to produce ATP.

25. Carbon Fixation CALVIN CYCLE CARBON FIXATION
The ATP and NADPH produced in the light reactions drive this stage
CARBON FIXATION
CO2 is incorporated into organic compounds, a process called carbon fixation

26. Carbon Fixation CALVIN CYCLE
Occurs in the stroma
Assisted by enzymes to produce three carbon sugars
Most three carbon sugars (PGAL) generated in the Calvin Cycle are converted to five carbon sugars (RUBP).
Some of the three carbon sugars leave the cycle and are used to make organic compounds that are stored as NRG for later

27. Calvin Cycle

28. Factors Affecting Photosynthesis
Light Intensity
Rate increases as light intensity increases
More electrons get excited in both photosystems!
Once all electrons are excited, the rate levels off.

29. Factors Affecting Photosynthesis
Carbon Dioxide Levels
Increasing levels of CO2 also stimulate photosynthesis until the rate levels off.

30. Factors Affecting Photosynthesis
Temperature
As temperature increases, photosynthesis increases to a maximum and then decreases with further increases in temperature.
Too high of a temperature will denature key enzymes!